Paleo-Climatology and Near-Extinction of Humans

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“Who would have thought that as recently as 70,000 years ago,
extremes of climate had reduced our population to such small
numbers that we were on the very edge of extinction.”
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Associated Press
Apr 24 06:15 PM US/Eastern

Study says near extinction threatened people
By RANDOLPH E. SCHMID
AP Science Writer

WASHINGTON (AP) – Human beings may have had a brush with extinction
70,000 years ago, an extensive genetic study suggests. The human
population at that time was reduced to small isolated groups in
Africa, apparently because of drought, according to an analysis
released Thursday.

The report notes that a separate study by researchers at Stanford
University estimated the number of early humans may have shrunk as
low as 2,000 before numbers began to expand again in the early Stone
Age.

“This study illustrates the extraordinary power of genetics to reveal
insights into some of the key events in our species’ history,”
Spencer Wells, National Geographic Society explorer in residence,
said in a statement. “Tiny bands of early humans, forced apart by
harsh environmental conditions, coming back from the brink to reunite
and populate the world. Truly an epic drama, written in our DNA.”

Wells is director of the Genographic Project, launched in 2005 to
study anthropology using genetics. The report was published in the
American Journal of Human Genetics.

Previous studies using mitochondrial DNA-which is passed down through
mothers-have traced modern humans to a single “mitochondrial Eve,”
who lived in Africa about 200,000 years ago.

The migrations of humans out of Africa to populate the rest of the
world appear to have begun about 60,000 years ago, but little has
been known about humans between Eve and that dispersal.

The new study looks at the mitochondrial DNA of the Khoi and San
people in South Africa which appear to have diverged from other
people between 90,000 and 150,000 years ago.

The researchers led by Doron Behar of Rambam Medical Center in Haifa,
Israel and Saharon Rosset of IBM T.J. Watson Research Center in
Yorktown Heights, N.Y., and Tel Aviv University concluded that humans
separated into small populations prior to the Stone Age, when they
came back together and began to increase in numbers and spread to
other areas.

Eastern Africa experienced a series of severe droughts between
135,000 and 90,000 years ago and the researchers said this
climatological shift may have contributed to the population changes,
dividing into small, isolated groups which developed independently.

Paleontologist Meave Leakey, a Genographic adviser, commented: “Who
would have thought that as recently as 70,000 years ago, extremes of
climate had reduced our population to such small numbers that we were
on the very edge of extinction.”

Today more than 6.6 billion people inhabit the globe, according to
the U.S. Census Bureau.

The research was funded by the National Geographic Society, IBM, the
Waitt Family Foundation, the Seaver Family Foundation, Family Tree
DNA and Arizona Research Labs.___

On the Net:

The Genographic Project: http://www.nationalgeographic.com/genographic

Copyright 2008 The Associated Press. All rights reserved.

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